There must be some multiplier that accounts for the width of the opening... in fact I think we went over that in a class and asked how the number was arrived at... have to check my notes.

The throat area is necessary for determination of PR

PRnet = (Vcc,ave * 3.66) / (RTtest * Acc)

My comment on those rain gauges was more for collecting enough water in problem areas, which are often times near sprinklers, and with respect to sprinkler types (ex. stream rotors) that IMO need a catch with a bigger throat opening to audit accurately.

Well, I have 1200 customers in my "current" list, meaning we have worked on their system in the last 3 years. I don't know how many homes we go to in a year, but we did over 800 blow outs last fall. So, somewhere between 900 and 1000 I assume. Let's say 1000. Of those, not all are "quality" customers, just one shot calls. So say 800. If we give 3 gauges to 400 of them, that is 1200 right there. I'm thinking of getting 1000 to start with and see how it goes.